A cruise control system refers to a system which uses various sensors such as a millimeter wave radar, a laser radar, or a vision sensor to track a preceding vehicle. Examples of the cruise control system include a smart cruise control system and an adaptive cruise control system.
The cruise control system uses information on a vehicle to be controlled and information on surrounding vehicles to estimate a heading direction of the vehicle to be controlled and determine a vehicle to be tracked. The function of the cruise control system is a very important factor for securing safety of the vehicle.
A method for estimating the heading direction of the vehicle varies depending on a control concept. Generally, a method which uses a steering angle signal, a method which uses a yaw rate signal, and a method which uses a lateral acceleration are representative.
According to the method which uses the steering angle signal, accuracy is lowered when the vehicle is being driven at a high speed. According to the method which uses the lateral acceleration signal, an accuracy is lowered when the vehicle is being driven at a low speed or passes a slope way. Accordingly, a method which uses the yaw rate signal which shows stable performance regardless of the speed of the vehicle is widely used.
In the method which uses the yaw rate signal, an accuracy of a yaw rate sensor significantly influences precise estimation of a heading direction of the vehicle. However, when the vehicle is being driven at a low speed, a value of the yaw rate sensor is significantly changed due to very tiny movement and the yaw rate sensor is very sensitive to a noise. Even though an electronic stability control (ESC) device corrects an offset of the yaw rate sensor, a precision required for the SCC system is very high so that a corrected value of the ESC device may not satisfy a SCC requirement performance. In the case of a yaw rate sensor to which an MEMS technique is applied, the offset varies depending on a temperature.
Korean Unexamined Patent Application Publication No. 2007-0060512 suggests a method for calculating an offset error of a yaw rate sensor to determine a trouble. However, even when the method is used, if the performance is deteriorated due to the temperature or the performance is temporarily lowered due to a noise, the offset of the yaw rate sensor cannot be corrected.